以下代码可以做到这一点：
用户在文本框中输入位置或位置，然后单击按钮。单击按钮时，将在用户输入的位置放置一个标记。不幸的是，这引发了一个空指针异常。
请帮我清除它。我已经包含了logcat中显示的错误。
错误在doInBackground((中，地址为null。
import android.content.Context;
import android.os.AsyncTask;
import android.support.v4.app.FragmentActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
import android.location.Address;
import android.location.Geocoder;
import java.util.List;
public class MapsActivity extends FragmentActivity implements GoogleMap.OnMapLongClickListener {
private GoogleMap mMap; // Might be null if Google Play services APK is not available.
LatLng latLng;
MarkerOptions markerOptions;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps2);
Button btn_find = (Button) findViewById(R.id.btn_find);
View.OnClickListener findClickListener = new View.OnClickListener() {
@Override
public void onClick(View v) {
// Getting reference to EditText to get the user input location
EditText etLocation = (EditText) findViewById(R.id.et_location);
// Getting user input location
String location;
location = etLocation.getText().toString();
if( !location.equals("")){
new GeocoderTask(getApplicationContext()).execute(location);
}
}
};
// Setting button click event listener for the find button
btn_find.setOnClickListener(findClickListener);
setUpMapIfNeeded();
}
private class GeocoderTask extends AsyncTask<String, Void, List<Address>> {
private Context mainContxt;
public GeocoderTask(Context con){
mainContxt=con;
}
@Override
protected List<Address> doInBackground(String... locationName) {
List<Address> geoResults=null;
Geocoder geocoder = new Geocoder(mainContxt);
try {
geoResults = geocoder.getFromLocationName(locationName[0], 1);
while (geoResults.size()==0) {
geoResults = geocoder.getFromLocationName(locationName[0], 1);
}
if (geoResults.size()>0) {
Address addresses = geoResults.get(0);
}
} catch (Exception e) {
System.out.print(e.getMessage());
}
// Creating an instance of Geocoder class
return geoResults;
}
@Override
protected void onPostExecute(List<Address> addresses) {
if(addresses==null ){
Toast.makeText(MapsActivity.this, "No Location found", Toast.LENGTH_LONG).show();
}
// Clears all the existing markers on the map
mMap.clear();
if(addresses!=null)
{ int t=addresses.size();
// Adding Markers on Google Map for each matching address
for(int i=0;i<t;i++){
Address address = addresses.get(i);
// Creating an instance of GeoPoint, to display in Google Map
latLng = new LatLng(address.getLatitude(), address.getLongitude());
String addressText = String.format("%s, %s",
address.getMaxAddressLineIndex() > 0 ? address.getAddressLine(0) : "",
address.getCountryName());
markerOptions = new MarkerOptions();
markerOptions.position(latLng);
markerOptions.title(addressText);
mMap.addMarker(markerOptions);
// Locate the first location
if(i==0)
mMap.animateCamera(CameraUpdateFactory.newLatLng(latLng));
}}}}
@Override
protected void onResume() {
super.onResume();
setUpMapIfNeeded();
}
/**
* Sets up the map if it is possible to do so (i.e., the Google Play services APK is correctly
* installed) and the map has not already been instantiated.. This will ensure that we only ever
* call {@link #setUpMap()} once when {@link #mMap} is not null.
* <p/>
* If it isn't installed {@link SupportMapFragment} (and
* {@link com.google.android.gms.maps.MapView MapView}) will show a prompt for the user to
* install/update the Google Play services APK on their device.
* <p/>
* A user can return to this FragmentActivity after following the prompt and correctly
* installing/updating/enabling the Google Play services. Since the FragmentActivity may not
* have been completely destroyed during this process (it is likely that it would only be
* stopped or paused), {@link #onCreate(Bundle)} may not be called again so we should call this
* method in {@link #onResume()} to guarantee that it will be called.
*/
private void setUpMapIfNeeded() {
// Do a null check to confirm that we have not already instantiated the map.
if (mMap == null) {
// Try to obtain the map from the SupportMapFragment.
mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map))
.getMap();
// Check if we were successful in obtaining the map.
mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
mMap.setOnMapLongClickListener(this);
if (mMap != null) {
setUpMap();
}
}
}
// An AsyncTask class for accessing the GeoCoding Web Service
private void setUpMap() {
}
@Override
public void onMapLongClick(LatLng latLng) {
mMap.addMarker(new MarkerOptions().position(latLng).title("Custom location"));
Toast.makeText(MapsActivity.this,"latlong is"+latLng, Toast.LENGTH_LONG).show();
}
}
**我的日志猫显示这个**
06-03 17:08:55.990 19880-19880/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.sweth.reached2.MapsActivity$GeocoderTask.onPostExecute(MapsActivity.java:143)
at com.example.sweth.reached2.MapsActivity$GeocoderTask.onPostExecute(MapsActivity.java:114)
at android.os.AsyncTask.finish(AsyncTask.java:602)
at android.os.AsyncTask.access$600(AsyncTask.java:156)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:615)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4441)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
at dalvik.system.NativeStart.main(Native Method)
您正在执行错误的if check
if(addresses==null || addresses.size()==0){
Toast.makeText(MapsActivity.this, "No Location found", Toast.LENGTH_LONG).show();
}
试着在上面这样做
if(addresses==null){
Toast.makeText(MapsActivity.this, "No Location found", Toast.LENGTH_LONG).show();
}
Null对象不应具有任何大小。您正在获取null地址，并检查null对象的大小。从而得到nullpointer exception
更新你也可以这样做
if(addresses==null){
Toast.makeText(MapsActivity.this, "No Location found", Toast.LENGTH_LONG).show();
}else{
if(addresses.size() == 0){
Toast.makeText(MapsActivity.this, "Zero Location found", Toast.LENGTH_LONG).show();
}else if(addresses.size() == 1){
Toast.makeText(MapsActivity.this, "one Location found", Toast.LENGTH_LONG).show();
}
}